Optimization for Multi-Cell NOMA Systems Assisted by Multi-RIS With Inter-RIS Reflection

Reconfigurable intelligent surface (RIS) and non-orthogonal multiple access (NOMA) are two promising technologies in future communication systems. The integration between RIS and NOMA has attracted the attention of researchers. However, NOMA hasn’t been investigated in multi-cell scenario assisted by multi-RIS with inter-RIS reflection. In this letter, we study the power minimization problem of an uplink multi-RIS assisted cooperative multi-cell NOMA network where RISs, with inter-RIS reflection, are deployed near both the BSs and users. Besides, a new NOMA scheme based on inter-group interference cancellation (IGIC) is proposed to further reduce interference from center users to edge users. Specifically, inter-group interference is eliminated by NOMA, while intra-group interference is mitigated by the joint design of equalizer, transmit power and RIS phase shift matrix. In the simulation stage, the minimum transmit power of different RIS deployment strategies and NOMA schemes are compared. The results show that our proposed scheme based on IGIC and multi-reflection RIS achieves lower total transmit power.